Search age:

Search in:

Dinosaurs in space

Geoff Maslen

ANDY Green is a youthful astronomy student from Swinburne University who found "living dinosaurs" in space — galaxies that were thought to have existed only in the far distant past. He recently co-authored a paper on the discovery that made the front page of world renowned science journal Nature.

PhD student Green says scientists were unaware the galaxies were still part of the present universe. They are extremely rare.

The Swinburne researcher called them living dinosaurs — the "Wollemi pines of space" — because they are galaxies no-one expected ever to find. Green says the galaxies look like disks and are reminiscent of the Milky Way, except they are physically "turbulent" and are in the process of forming many young stars.

Research team leader and Green's supervisor Karl Glazebrook says such galaxies were thought to exist up to 10 billion years ago when the universe was less than three quarters its present age.

Advertisement

Professor Glazebrook says that as stars form from gas, astronomers had proposed that the extremely fast star formation in the just-discovered ancient galaxies was fuelled by some special mechanism — that such a mechanism only existed in the early universe when cold streams of gas were continually falling in to the galaxies.

He says that discovering the same kind of galaxy in today's universe meant that mechanism was not the only way such rapid star formation was fuelled — when young stars form, they create turbulence in the surrounding gas and the more stars that are forming, the more turbulence the galaxy experiences.

"Turbulence affects how fast stars form, so we're seeing stars regulating their own formation," Green says. "It's a bit like a little girl deciding how many siblings she should have yet we still don't know where the gas to make these stars comes from."

He says understanding the ways stars form was one of the most basic but still unsolved problems of astronomy. The discovery of the ancient galaxies has changed astronomers' ideas about how star formation is fuelled.

The Swinburne study was based on selected galaxies from the Sloan Digital Sky Survey, a census of modern galaxies.

The survey began in 2000 and will map 25 per cent of the sky, scanning 100 million stars, galaxies and other objects as well, and the spectra of 1 million.

Green's study involved an international team of astronomers. As well as those researchers at Swinburne's centre for astrophysics and supercomputing, the team included members of the research school of astronomy and astrophysics at the Australian National University, the astronomy department at the University of Toronto , the observatories of the Carnegie Institution of Washington in Pasadena, California, and the Australian Astronomical Observatory in NSW.

In their report in Nature, the researchers said that observations of star formation and turbulence in early galaxies at high spatial and spectral resolution have shown that two-thirds are massive rotating disk galaxies, and the remainder less massive non-rotating objects.

"The line-of-sight-averaged velocity dispersions are typically five times higher than in today's disk galaxies," the team wrote. "This suggests that gravitationally unstable, gas-rich disks in the early universe are fuelled by cold, dense accreting gas flowing along cosmic filaments and penetrating hot galactic gas halos."

"These accreting flows, however, have not been observed and cosmic accretion cannot power the observed level of turbulence. Our observations were of a sample of rare, high-velocity-dispersion disk galaxies in the nearby universe where cold accretion is unlikely to drive their high star-formation rates.

"We found their velocity dispersions are correlated with their star-formation rates but not their masses or gas fractions. This suggests that star formation is the energetic driver of galaxy disk turbulence at all cosmic epochs."

As part of his research Green spent time at the Anglo-Australian Telescope and the ANU's 2.3-metre telescope at the Siding Spring Observatory in the Warrumbungle Mountains in New South Wales.

Matthew Colless, Director of the Australian Astronomical Observatory at Siding Springs, says the study has highlighted the value of large telescopes. "They are ideal for studying in detail the nearby counterparts of galaxies seen in the distant universe by eight and 10-metre telescopes," Professor Colless says.

For the next stage of his research, Green will use the largest optical telescope in the world at the Keck Observatory in Hawaii to take a closer look at the rare galaxies he has discovered.

"Really, we need a bigger telescope, such as the Giant Magellan Telescope, to understand star formation," he said. "But, until it's constructed, Keck is the best tool available."

Green left Melbourne last month to undertake further research at the Keck Observatory. This has been made possible because of an agreement Swinburne has with the California Institute of Technology, which operates the observatory. The agreement provides Swinburne astronomers with access to the observatory for up to 20 nights a year.

But Green will have to wait another eight years before he stands a chance of getting access to the Giant Magellan Telescope. Larger than any other telescope ever built, it will be located at the Las Campanas Observatory in Chile's Atacama Desert and is not likely to be completed before 2018.

The Magellan Telescope telescope will use seven mirror segments, each 8.4 metres in diameter, arranged to form a single optical surface. This will give the telescope the resolving power of a 24.5-metre primary mirror.

It is expected to have more than four times the light-gathering ability of existing instruments and will produce images up to 10 times sharper than the Hubble Space telescope. Magellan should be able to answer many of the questions at the forefront of astrophysics today, including the mysteries behind the strange ancient disk galaxies Green has discovered.